Just curious, does BF get money for just rendering ads, or only for (or more for?) clickthrough? (Or only for (more for?) eventual purchase from advertiser?)

If my beloved BF gets money from clickthrough, I will start clicking and checking out advertisers stuff more often (when the automatic stuff actually throws relevant ads at me). But if BF gets all the money it gets just from displaying ads (not more for clickthrough), I will be less likely to click.